As compared with conventional liquid display panels, Organic Light Emitting Diode (OLED) display panels have advantages such as faster response speed, better color purity and higher brightness, higher contrast ratio and wider view angle, and thus have attracted more attentions from developers of display technologies.
FIG. 1 is a pixel circuit of a conventional light emitting device. The pixel circuit includes: a first transistor T1 having a control terminal electrically coupled to a first scan signal S1 and a first terminal electrically coupled to an input voltage Vint; a second transistor T2 and a third transistor T3, the control terminals of which are electrically coupled to a second scan signal S2; a fourth transistor T4 having a control terminal electrically coupled to a control signal EM; a fifth transistor T5, a control terminal of the fifth transistor T5, a second terminal of the first transistor T1 and a first terminal of the second transistor T2 being electrically coupled to a node B together; a sixth transistor T6 having a control terminal electrically coupled to a control signal EM; a capacitor Cst having a first terminal electrically coupled to a first power voltage ELVDD and a second terminal electrically coupled to the control terminal of the fifth transistor T5. A first terminal of a light emitting diode such as an OLED and a second terminal of the sixth transistor T6 are electrically coupled to a node A, and a second terminal of the light emitting diode D is electrically coupled to a second power voltage ELVSS.
When the first scan signal S1 and the second scan signal S2 are at a high level VGH and the control signal EM is at a low level VGL, the fourth transistor T4 to the sixth transistor T6 are turned on, the first transistor T1 to the third transistor T3 are turned off, and the OLED emits light. At this time, there exist two current leakage paths in the circuit: in the first current leakage path, the current flows to the input voltage Vint via the first transistor T1 (the first path is referred to as a Vint current leakage path), and in the second current leakage path, the current flows to the light emitting diode via the second transistor T2 and the sixth transistor T6 (the second path is referred to as an Anode current leakage path). The two current leakage paths cause reduction in the capacitance value of the capacitor Cst, thereby resulting in decreased holding capability of the Cst and potential reduction across the Cst. Consequently, the gate voltage drop of the fifth transistor T5 becomes larger. As the capacitance value is reduced, the holding capability of the capacitor Cst becomes weaker, and this can result in worse image flicker under a low frequency (typically, lower than 60 Hz), and thus the reliability of displayed images can be influenced.
At present, in order to reduce the image flicker, adjustments have been made from both design and process aspects to increase the capacitance value and thereby to enhance the reliability of images. However, by doing this, new problems occur: if design rules are violated or the adjustments in design are too aggressive, symmetry and matching state of other devices may be influenced; also, as the thickness of the sandwiched capacitor dielectric is reduced, the process becomes more difficult, and new problems with the structures of other relevant layers may arise.
Thus, there is a need for a new pixel circuit and a method for driving the same.
It should be noted that, information disclosed in the above background portion is provided only for better understanding of the background of the present disclosure, and thus it may contain information that does not form the prior art known by those of ordinary skill in the art.